Fibrin sealants are a type of surgical “glue” that is made from human blood-clotting proteins, and that is typically used during surgery to control bleeding. The ingredients in these sealants interact during application to form a stable clot composed of a blood protein fibrin. Fibrin sealants are presently used during surgery for several different purposes: to control bleeding in the area where the surgeon is operating, to speed wound healing, to seal off hollow body organs or cover holes made by standard sutures, to provide slow-release delivery of medications to tissues exposed during surgery.
Fibrin sealants generally consist of two human plasma-derived components: (a) a highly concentrated Fibrinogen Complex (FC) composed primarily of fibrinogen and fibronectin along with catalytic amounts of Factor XIII and plasminogen and (b) a high potency thrombin. Fibrin sealants may also contain aprotinin. By the action of thrombin, (soluble) fibrinogen at first is converted into fibrin monomers which aggregate spontaneously and form a so-called fibrin clot. Simultaneously, factor XIII (FXIII) present in the solution is activated by thrombin in the presence of calcium ions to factor XIIIa. The aggregated fibrin monomers and any remaining fibronectin possibly present are cross-linked to form a high polymer by new peptide bonds forming. By this cross-linking reaction, the strength of the clot formed is substantially increased. Generally, the clot adheres well to wound and tissue surfaces, which leads to the adhesive and haemostatic effect. (U.S. Pat. No. 7,241,603). Therefore, fibrin adhesives are frequently used as two-component adhesives which comprise a fibrinogen complex (FC) component together with a thrombin component which additionally contains calcium ions.
A particular advantage of a fibrin sealant is that the adhesive/gel does not remain at its site of application as a foreign body, but is completely resorbed just as in natural wound healing, and is replaced by newly formed tissue. Various cells, e.g., macrophages and, subsequently, fibroblasts migrate into the gel, lyse and resorb the gel material and form new tissue. Fibrin sealants have been used to form fibrin gels in situ, and these fibrin gels have been used for delivery of cells and growth factors (Cox et al., Tissue Eng 10:942-954, 2004; Wong et al., Thromb Haemost 89:573-582, 2003).
For tissue repair, it is desirable to localize growth factors and cells in a matrix such as a fibrin gel. For example, fibrin gel has been used for delivery of TGF-β in various complex mixtures including fetal bovine serum, coral granules, and liposomes (Fortier et al., Am J Vet Res 58(1): 66-70, 1997; Arnaud et al., Chirurgie Plastique Esthetique 39(4): 491-498, 1994; Arnaud et al. Calcif Tissue Int 54: 493-498, 1994; Giannoni et al., Biotechnology and Bioengineering 83(1): 121-123, 2003). Alternative means to deliver growth factors from fibrin gels involve conjugates comprising transglutaminase substrates, antibodies, and VEGF fragments bound to the growth factors (See, for example U.S. Pat. No. 6,506,365; U.S. Pat. No. 6,713,453 and US Patent Publication 2003/0012818, incorporated herein by reference in their entirety). See also US patent application 20030012818 which describes drug delivery matrices to enhance wound healing. Additionally, fibrin gels have been shown to induce cell growth (e.g., human mesenchymal stem cell (HMSC)) and proliferation as well as, to some extent, osteogenic differentiation, depending on the concentrations of FC and thrombin in the matrix (Catelas et al., Tissue Eng 12:2385-2396, 2006).
The ability of fibrin sealants to deliver growth factors to a particular site in the body can be beneficial, but proper regrowth of tissue often requires a continuous/steady supply of growth factor or cytokine delivered at a specific rate to the site so that proper treatment is ensured. This is especially true if the therapeutic protein has a short half-life in vivo. Fibrin sealants currently in use provide for some delayed release of the seeded drug or agent, but the ability to extend the life of the agent in the sealant would improve the long-term tissue repair in vivo.
Thus, there remains a need in the art to develop an effective means to deliver growth factor in vivo for treatment of various conditions and disorders, to develop improved methods for controlled release of growth factors from a fibrin gel.